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By Richard Webb (Image: Andy Smith) Image: Andy Smith WHAT is a boojum? Is it: a particularly dangerous variety of snark; a bizarre cactus-like tree endemic to Baja California in Mexico; or a geometrical pattern sometimes seen on the surface of superfluid helium-3? In fact it’s all three. Fans of Lewis Carroll will recall that in his poem The Hunting of the Snark, boojums are the most feared of all snarks. Meagre and hollow, but crisp-tasting beasts, they inhabit desolate valleys – a bit like the Mexican tree. Carroll’s boojums cause those who venture too close to “softly and suddenly vanish away” – a fate that also befalls helium’s superfluidity when a boojum appears. Meagre and hollow, but crisp-tasting beasts, they inhabit desolate valleys The names have come about thanks to science’s long tradition of allowing individuals to name discoveries as they see fit. The Mexican succulent owes its moniker to the English-born botanist Godfrey Sykes. On spying his first example in 1922, he reportedly snorted, in the spirit of Carroll’s snark hunters, “Ho ho, a boojum!” Half a century later, in an age less accommodating of eccentricity, physicist David Mermin of Cornell University in Ithaca, New York, had to employ a good deal more stealth and guile to establish his superfluid tribute to Carroll. Part of his motivation, he admits, was putting one over on journal editors, but he had a more constructive reason too: “It’s nice to have names for things that are suggestive,” he says. These days,